Conventional internal combustion engines are typically lubricated with a mechanical pump powered by the engine via belts or gears. The speed of the pump, and therefore the oil pressure and rate of oil flow, are a function of the engine speed. Auxiliary electrically operated oil pumps have been used to operate at engine start-up to ensure oil flow to the engine as soon as possible.
Oil not only lubricates engine parts, but oil is also important in engine cooling. It is important that sufficient oil pressure be provided to float the engine bearings and prevent metal-to-metal contact. With the use of a mechanical oil pump powered by the engine, the amount of lubrication and cooling of the engine is dependent on engine speed and is not relative to the work load of the engine.
U.S. Pat. No. 5,884,601 to Robinson discloses a variable speed electric pumping system that controls the speed of an electric oil pump based on engine load. Engine load is determined by monitoring an engine speed signal received from an engine RPM sensor. Robinson also discloses receiving an oil pressure signal from an oil pressure sensor and controlling the oil pump speed to maintain a designed specification oil pressure. Robinson discloses that this compensates for the tendency of the oil pressure to decrease as the engine wears.
The disclosure of Robinson, however, does not describe any method of determining engine load other than by sensing engine speed from an engine RPM sensor. Sensing engine RPM is often an inadequate method for determining the load on an engine and for determining the lubrication requirements of the engine. For example, a truck traveling up a steep hill at a given engine RPM may have a much higher torque on the engine than the same truck traveling down a hill at the same engine RPM. The torque on the truck engine traveling uphill will be much higher and, consequently, there will be more force exerted on the engine bearings and the engine bearings will be more prone to wear. Thus, an oil pump control system that controls the oil pump based solely on engine RPM will not be able to provide adequate lubrication to an engine under all load conditions without wasting a significant amount of pumping energy.
The present invention provides a fluid delivery control system that avoids some or all of the aforesaid shortcomings in the prior art.